Measles virus (MV) infection in the central nervous system (CMS) is associated with neuropathological disorders, such as subacute sclerosing panencephalitis (SSPE), in which the immune system fails to control MV replication in the brain. Our laboratory uses a transgenic mouse model of CNS-restricted MV infection via targeted neuronal expression of one of the measles virus receptors (CD46) to study interactions between MV-infected neurons and the immune response. In this model, adult mice successfully clear MV from neurons in the brain by mounting an immune response that requires interferon-gamma (IFN?) and involves T-cell recruitment to the CNS, whereas MV-infected neonates recruit similar levels of T-cells to the brain, but are unable to control MV replication in neurons, develop extensive neuropathology, and rapidly succumb to MV infection. While IFN? is necessary for MV clearance from neurons in adult brains in vivo, IFN? triggers a distinct signaling cascade in primary cultured neurons in comparison to the more extensively studied fibroblasts and cell lines. A paradox emerges from these preliminary observations: how does IFN? mediate viral clearance from neurons, when the canonical signaling components (as measured by phosphorylation/activation of the transcriptional activator STAT1) are restricted? We hypothesize that limited STAT1 activation by IFN? in neurons contributes to viral clearance, but that other signaling pathways contribute to anti-viral activity in neurons. To address this hypothesis, Aim 1 dissects the mechanisms IFN?-mediated MV clearance in explanted primary hippocampal neurons in vitro. Through western blot, confocal imaging, and quantitative RT-PCR, the intrinsic ability of primary neurons to mediate viral clearance will be addressed independently of the complicating contribution of glial cells found in mixed CNS cultures. Aim 2 will extend the observations made in primary cultured neurons by establishing the role of IFN? signal transduction in the complicated microenvironment of the brain in vivo. These studies will be aided by genetically modified mice (e.g. IFN? knockouts, STAT1 knockouts) and will allow us to address the age-dependence of neuropathogenesis. By determining the role of IFN? signaling in MV clearance in neurons, these studies will clarify how IFN? triggers anti-viral defense mechanisms in a unique, non-renewable cell type, but also aim to provide a mechanism for the cell-specific heterogeneity of responses to IFN?. In addition, these studies will also address how intrinsic developmental neuronal properties play a role in dictating whether or not viral clearance occurs in CNS neurons.